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The purpose of the Alkalinity protocol is to measure the amount of alkalinity dissolved in a water sample. Alkalinity is closely related to the kinds of aquatic life that will survive in water. If the alkalinity of a body of water is too high, organisms will die. The alkalinity of water is measured by the degree to which the water sample can neutralize acid. If the water sample is very alkaline, it will take less to neutralize an acid.
- Step 1 - Calibration and Quality Control: Preparing the Baking Soda Standard
Before measuring the alkalinity of a water sample, students must prepare a baking soda standard whose alkalinity is 68 mg/L as CaCo3. In order to do this, students will measure out a solution of baking soda dissolved in water according to the instructions as listed on the Alkalinity Protocol site in the GLOBE Teacher’s Guide.
- Step 2 - Alkalinity Measurment
Students measure the alkalinity in a water sample using an alkalinity tool that meets the GLOBE Instruments Specifications. This procedure involves the addition of a color indicator to the water sample that will cause the color in the water sample to change to the degree of alkalinity present in the water. Students must then add drops of an acid titrant (Hydrochloric Acid) until a color change is observed. The amount of alkalinity is calculated from the volume of Hydrochloric Acid necessary to make the color disappear.
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Alkalinity Test Kit
Baking soda (sodium bicarbonate)
Distilled water bottle
Distilled water
500 mL beaker
100 mL graduated cylinder
500 mL graduated cylinder
Stirring rod
Data sheets
Sample bottle
Latex gloves/safety goggles
Balance
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Students should wear the appropriate safety equipment listed and follow carefully all safety instructions specified by your test kit, including any accompanying Material Safety Data Sheets.
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1) A student pours a baking soda solution into a graduated cylinder.
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2) Students wear latex gloves and safety goggles when working with the alkalinity test kit.
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3) The student adds a color indicator to the water sample.
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![Protocols [Image: Blue-Eyed Grass]](images/protocols_h.jpg)
